I9I4.] CONCEPTION AND TRINITY BAYS, NEWFOUNDLAND. 449 



of Conception and Trinity Bays may be of interest at this point as 

 illustrating the manganese content of some of the rocks which are 

 most like those existing during the formation of the deposits : 



MnO. 



Monzonite, Woodford 19 



Quartz porphyry, Manuals 11 



Conception sL, Random Is 12 



Granite, Manuels 13 



Aporhyolite, Manuels 12 



Basalt, Blue Hills 48 



Analyst, A. F. Buddington. 



Similar analyses have been made from the rocks of the Clyde pre- 

 Cambrian drainage area and show from .1 to .7 of a per cent, of 

 MnO (Murray and Irvine, 19: 722). In all probability then the 

 pre-Cambrian rocks on the east and west of the Cambrian basin 

 were the ultimate source of the manganese. 



Summary of Genesis of Manganese. 



Ultimate Source of the manganese was the manganese-bearing 

 silicates of pre-Cambrian igneous and metamorphic rocks east and 

 west of the Cambrian Sea. 



Solution of manganese-bearing silicates and conversion of the 

 manganese into the soluble bicarbonate; under favorable conditions 

 oxides of manganese resulted from the oxidation of the bicarbonate 

 of manganese. 



Transportation of the manganese chiefly as the bicarbonate and 

 to a less extent as suspended particles of oxides by pre-Cambrian 

 drainage systems to Cambrian basins. 



Concentration of the salts of manganese chiefly as the bicar- 

 bonate in the sea-water immediately overlying the deposited muds. 



Precipitation of manganese carbonate from solution through 

 liberation of CO, from the bicarbonate, or of the oxide. 



Clastic Origin of Some Manganese. — While the main contribu- 

 tion of the manganese came from the pre-Cambrian drainage area 

 in solution undoubtedly the deposited muds supplied a minor 

 portion. 



